The present invention relates to intraluminal radiation delivery (IRT) devices and more particularly to an over-the-wire brachytherapy catheter. Also provided are methods for delivering localized radiation in vivo.
Stenosis is a narrowing or constriction of a duct or canal. A variety of disease processes, such as atherosclerotic lesions, immunological reactions, congential abnormalities and the like, can lead to stenoses of arteries or ducts. In the case of stenosis of a coronary artery, this typically leads to myocardial ischemia. Percutaneous transluminal coronary angioplasty (PTCA), the insertion and inflation of a balloon catheter in a coronary artery to affect its repair, is widely accepted as an option in the treatment of obstructive coronary artery disease. In general, PTCA is used to increase the lumen diameter of a coronary artery that is partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. In PTCA, a coronary guiding catheter provides a channel from outside the patient to the ostium of a coronary artery. Then, a balloon catheter is advanced over a small diameter, steerable guidewire through the guiding catheter, into the artery, and across the stenosis. The balloon is inflated to expand the narrowing. Dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten abrupt reclosure of the dilated vessel or even perforations in the vessel wall. To treat or prevent such sequelae, tubular stents are often placed within the angioplasty site to scaffold the vessel lumen.
Other invasive vascular therapies include atherectomy (mechanical removal of plaque residing inside an artery), laser ablative therapy and the like. While the stenosis or occlusion is greatly reduced using these therapies, many patients experience a recurrence of the stenosis over a relatively short period. Restenosis, defined angiographically, is the recurrence of a 50% or greater narrowing of a luminal diameter at the site of a prior therapy. Additionally, researchers have found that angioplasty or placement of a stent in the area of the stenosis can irritate the blood vessel and cause rapid reproduction of the cells in the medial layer of the blood vessel, developing restenosis through a mechanism called medial hyperplasia. Restenosis is a major problem which limits the long-term efficacy of invasive coronary disease therapies. Additionally, the rapid onset of restenosis is compounded by the lack of ability to predict which patients, vessels, or lesions will undergo restenosis.
Although the mechanism of restenosis is not fully understood, clinical evidence suggests that restenosis results from a migration and rapid proliferation of a subset of predominately medially derived smooth muscle cells, which is apparently induced by the injury from the invasive therapy. Such injury, for example, is caused by the angioplasty procedure when the balloon catheter is inflated and exerts pressure against the artery wall, resulting in medial tearing. It is known that smooth muscle cells proliferate in response to mechanical stretch and the resulting stimulation by a variety of growth factors. Also, intimal hyperplasia can contribute to restenosis, stimulated by the controlled therapeutic injury. It is believed that such proliferation stops one to two months after the initial invasive therapy procedure but that these cells continue to express an extracellular matrix of collagen, elastin and proteoglycans. Additionally, animal studies have shown that during balloon injury, denudation of endothelial cells can occur, followed by platelet adhesion and aggregation, and the release of platelet-derived growth factor (PDGF) as well as other growth factors. As mentioned above, this mass of tissue can contribute to the re-narrowing of the vascular lumen in patients who have restenosis. It is believed that a variety of biologic factors are involved in restenosis, such as the extent of the tissue injury, platelets, inflammatory cells, growth factors, cytokines, endothelial cells, smooth muscle cells, and extracellular matrix production, to name a few.
It has been found that irradiating the blood vessel walls at the treatment site can reduce or prevent hyperplasia. Precise control over the amount of radiation is important, since insufficient radiation will not prevent restenosis and excessive radiation can further damage the blood vessel or surrounding tissues. To prevent unnecessary radiation beyond the site of the stenosis, it is preferable to introduce a small radiation source into the treated vessel. The prior art contains numerous examples of radiation catheters and source wires for this purpose.
One prior art device describes a catheter having a spherical inflatable chamber adjacent the catheter distal end. A fluid containing a radioactive material such as radioactive iodine is pumped into the chamber, inflating the chamber and treating the vessel walls with ionizing radiation. The chamber will stop blood flow, so it can be inflated only for a short time. Further, precisely controlling radiation exposure and fully draining the chamber to end treatment are very difficult.
Another prior art catheter includes radiation means positioned in an elongate, flexible carrier. The carrier lacks any provision for steering or for over-the wire guidance, which is necessary for negotiating tortuous and branching vessels. Another prior art device mounts a radiation source distally on or within a guidewire.
Other prior art catheters include one or more balloons used to center a radiation source within the vessel. Irradiating a segment of an artery or the like generally takes from about 3 to 45 minutes. Since a balloon typically occludes, or shuts off blood flow through an artery, treatment can be conducted for only short periods before ischemia or tissue damage from lack of blood flow becomes significant. To solve this problem, some balloon-centered radiation catheters include a bypass, or perfusion feature, so that blood continues to flow through the artery during treatment. In some devices, the perfusion feature is provided by mounting a helical centering balloon around the catheter shaft. During radiation treatment, the helical balloon is inflated to center the catheter shaft in the vessel and to allow blood to flow through the spiral channel formed between the helical turns of the balloon. In alternative prior art devices, the catheter shaft is mounted off-center within a helical balloon such that blood can flow through the center of the helix.
Yet another prior art radiation catheter includes a first guidewire lumen, a second blind lumen to receive a radiation source wire, and an inflatable centering member that permits blood flow therethrough during radiation treatment. However, since the two lumens extend parallel to each other and to the axis of the catheter, the guidewire will block radiation from the source wire, forming a linear shadow along the wall of the vessel. This shadowing phenomenon typically requires that the guidewire be withdrawn from the treatment site to ensure that radiation emitted by the source is not blocked by the guidewire. Withdrawing the guidewire adds time to the procedure. Also, when using a rapid-exchange type catheter, with the attendant short guidewire lumen, withdrawing the guidewire brings the risk of having the guidewire slip out of the catheter completely. In this untoward event, the guidewire cannot be reinserted into the catheter without removing both devices from the patient.
With the above in mind, it is an object of the invention to provide an over-the-guidewire radiation catheter that can deliver a shadow-free dose of therapeutic radiation to a treatment site without requiring withdrawal of the guidewire.
The present invention is a transluminal, over-the-wire catheter that provides a lumen for guiding a radiation source wire to an intended treatment site within a patient. With the removable radiation source wire in place, the catheter provides shadow-free irradiation of an intended vessel wall without having to move or withdraw the guidewire. Although the guidewire lies within the radiation pattern emitted by the radiation source wire, the guidewire does not cast a linear radiation shadow on the vessel wall because the guidewire and the radiation source wire are arranged in a parallel double helix configuration. The catheter of the invention includes a first lumen for the guidewire and a second lumen for the radiation source wire. The two lumens are twisted together to form the desired parallel double helix configuration for the guidewire and the radiation source wire.
An optional embodiment of the invention provides a centering mechanism to keep the double helix configuration centered in the vessel being treated. The centering mechanism may be an inflatable balloon mounted around the catheter shaft adjacent the distal end of the catheter. The balloon is inflated through a third lumen that extends from the proximal end of the catheter to the balloon. The centering balloon may comprise a single elongate balloon, which may be a dilatation balloon. Other centering balloons may be a helical or spiral balloon, a multi-lobed balloon, or two or more short, catenated balloons. Some of these balloon variations are better suited for treatment in a vessel having a tight radius bend, and others permit perfusion of blood past the centering mechanism, both concepts being understood by those of skill in the art of radiation catheters. Other optional centering mechanisms may include wire braid structures or wire hoops mounted about the double helix configuration at the distal end of the catheter.
The catheter of the invention may also incorporate a dilatation balloon mounted about or adjacent to the double helix configuration. In this alternate embodiment, the balloon may be used to perform angioplasty before, or concomitantly with intravascular radiotherapy provided from the double helix configuration.
Although catheters in accordance with the invention are well suited for the treatment of coronary arteries, any body lumen can be treated by a medical device of the present invention, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver or larger, peripheral arteries.